CHAPTER 33

PERSPECTIVES ON SPECIFIC SUBSTANCES: CHLORINE Richard Lawuyi and Merv Fingas Emergencies Science Division, Environment Canada, Environmental Technology Centre, River Road, Ottawa, Ontario

33.1

OVERVIEW OF PRODUCT AND INDUSTRIAL USES Chlorine is a greenish-yellow gas that is 2.5 times heavier than air. It does not occur naturally as a gas. It makes up about 0.0314% of the earth’s upper crust, where it exists mainly in the form of sodium, potassium, and magnesium chlorides. The major proportion is present in the oceans, constituting about 2%. For many decades, the growth in chlorine use has often been equated with the strength of a nation’s economy. This is largely due to the various chemical industries and chemical products that are often generated. The most important sources of man-made emissions and releases of chlorine into the environment are those involving its production, transportation, handling, and use. Chlorine was placed second in a priority list ranking of hazardous chemicals determined by the Emergencies Branch of Environment Canada (Fingas et al., 1991). Some of the criteria used in ranking chemicals are historical spill volume, supply volume, reported spill frequencies, and toxicity, including persistence and bioaccumulation. This substance should therefore be of great concern.

33.1.1

Modern Industrial Uses

The largest use of chlorine is in plastics. As shown in Fig. 33.1, chlorine is used extensively in the manufacture of several chlorinated aliphatic solvents, organic and inorganic intermediates, plastics, and in the pulp and paper industry (CIS, 1999). Chlorine and chlorine dioxide are still used in the bleaching of pulp, although to a lesser degree than in the past in order to reduce the potential for the formation of polychlorinated dioxins. The disinfection of drinking and wastewater, sewage, and biofouling in cooling and power plants represent other important uses of chlorine. The complex chemistry and implications for the environment will be discussed later.

33.2

INTRODUCTION Chlorine does not occur naturally except during volcano eruptions, but it is found combined with metals in the form of sodium, potassium, and magnesium chlorides. Chlorides make 33.1

33.2

CHAPTER THIRTY-THREE

FIGURE 33.1 Major uses of chlorine.

up approximately 0.0314% of the earth’s upper crust. A substantial portion is found in the oceans, which contain about 2% chloride. Some chlorides are also present in the atmosphere in the form of aerosols. Chlorine gas finds its way into the environment during production and use, as well as from accidental releases during transportation and handling. Chemical spills occur frequently in Canada and most other countries in the industrialized world. These spills often involve very large volumes of chemicals. Many spills happen in stationary facilities, and only a small proportion occur during transfers or while in transit. In Canada between 1974 and 1984, 36 major spills of chlorine were recorded in the NATES (National Analysis of Trends in Emergencies System), involving about 121 tons of liquefied chlorine (Environment Canada, 1999). According to the DGAIS (Dangerous Goods Analytical Information System) database, there were about 24 major chlorine spills in 1991. This is shown in Table 33.1. According to the 1993 National Pollutant Release Inventory, 4,859 tons of chlorine were released in 1993. TABLE 33.1 Spill Profile of Chlorine in Canada

Year

Number of spills

Quantity (tons)

1974–84 1985 1986 1987 1988 1989 1990 1991

36 9 18 19 4 5 8 24

121 2,146 414,000 49,802 9 0 11 –

PERSPECTIVES ON SPECIFIC SUBSTANCES: CHLORINE

33.3

33.3.1

33.3

PHYSICAL AND CHEMICAL PROPERTIES AND SUMMARY OF GUIDELINES Physical State Properties

At room temperature, chlorine is a pungent, greenish-yellow, nonflammable gas with a distinctive irritating odor. It is about 2.5 times as heavy as air. On the other hand, chlorine liquid is a clear amber color and about 1.5 times as heavy as water (CGA, 1990). Common name: Chlorine Molecular formula: Cl2 Atomic weight: 35.453 Molecular weight: 70.906 CAS number: 7782-50-5 UN number: 1017 RTECS number: F02100000 Labels: Corrosive gas Specific hazards: Corrosive Synonyms and Trade Names (RTECS On-Line, 2000): Bertholite Chloor Chlor Chlore Cloro Chlorine mol Molecular chlorine Grades and purities (Braker and Mossman, 1980):

33.3.2

Grade

Minimum purity, mole % (liquid phase)

Research Ultrahigh purity High purity

99.96 99.9 99.5

Physical Data (all information from Braker and Mossman, 1980, unless noted otherwise)

Usual shipping state: Liquefied gas under its own vapor pressure, 590 kPa, (21.1⬚C) Physical state at room temperature and pressure: Gas Melting point (1 atm): ⫺100.98⬚C (CGA, 1990) Boiling point (101.325 kPa): ⫺34.05⬚C ⫺34.6⬚ (Lide, 1999) Vapor pressure (21.1ⴗC): 689.0 kPa Densities: Absolute density, gas at 101.325 kPa and 20⬚C: 2.9800 kg / m3 Relative density, gas at 101.325 kPa and 25⬚C, (air ⫽ 1): 2.473

33.4

CHAPTER THIRTY-THREE

Density, liquid at saturation pressure and ⫺40⬚C: 1,574 kg / m3 Specific gravity of gas at 0⬚C and 1 atm (air ⫽ 1): 2.485 (CGA, 1990) Density, 0⬚C: 3.214 kg / m3 (Lide, 1999) Fire properties (from CGA, 1990): Flammability: Nonflammable classification by U.S. DOT Behavior in fire: Will support combustion of some materials Other properties: Molecular weight: 70.90540 (Lide, 1999) Grades (minimum purity % chlorine): Research 99.96% Ultrahigh purity 99.9% High purity 99.5% Refractive index: Gas, 1.000713 at 25⬚C and 101.325 kPa 1.000768, gas (Lide, 1999) 1.367, liquid (Lide, 1999) Viscosity: Gas, 0.01327 mPa 䡠 s at 20⬚C and 101.325 kPa Liquefied, 0.385 mPa 䡠 s at 0⬚C Surface tension, 0⬚C: 21.90 mN / m Latent heat of fusion at ⫺100.98⬚C: 90.341 kJ / kg Latent heat of vaporization at ⫺34.05⬚C: 287.84 kJ / kg Specific heat dry gas (⫺1.1 to 27⬚C at or below 100 psia): Cp 0.473 kJ / kg 䡠 ⬚C (CGA, 1990) Cv 0.348 kJ / kg 䡠 ⬚C Specific heat ratio (gas 101.325 kPa, 25⬚C) Cp / Cv: 1.308 Critical temperature: 144⬚C Critical pressure: 7,710 kPa Critical volume: 1.745 dm3 / kg Critical density: 0.573 kg / dm3 Critical compressibility factor: 0.276 Triple point temperature: ⫺34.05⬚C Specific volume (21.1⬚C, 101.325 kPa): 337.1 dm3 / kg Thermal conductivity, gas (26.7⬚C, 101.325 kPa): 0.0088 W / m 䡠 ⬚K Solubility in water (0⬚C, 101.325): 4.610 cm3 / cm3 of water 0⬚C: 1.46 g / 100 cc of water (liquid) (Lide, 1999) 10⬚C: 310 cc / 100 cc of water (gas) (Lide, 1999) 30⬚C: 177 cc / 100 cc of water (gas) (Lide, 1999) 30⬚C: 0.57 g / 100 cc of water (liquid) (Lide, 1999) Solubility in other solvents: Alkali (Lide, 1999) Diffusivity: 1.44 ⫻ 10⫺5 cm2 / s (water, 25⬚C) (Perry et al., 1984) Some physical constants of the chlorine atom (Cl) (Bailar et al., 1975): Property: Values Mass number of naturally occurring isotopes: 35 (75.77%) 37 (24.23%) 35.453 Atomic number: 17 Electronic configuration and ground state: [Ne]3s2 3p5 First ionization potential (kcal): 299 Electron affinity at 298⬚K (kcal): 84.8

PERSPECTIVES ON SPECIFIC SUBSTANCES: CHLORINE

33.5

Electronegativity: 3.0 Dissociation energy of Cl2 molecule at 298⬚K, D(X2)(kcal): 58.0 Thermodynamic properties: ⌬Hƒ⬚ [X(g)] at 298⬚K (kcal): 28.989 ˚ ): 0.99 Single-bond covalent radius (A ˚ ): 1.82 Ionic radius of X⫺ ion (NaCl structure) (A ⌬Hƒ⬚ [X⫺ (g)] at 298⬚K (kcal): ⫺55.7 ⌬H ⬚hydration [X⫺ (g)] at 298⬚K (kcal g ion⫺1): ⫺88 E⬚ (0.5X2 / X⫺), aqueous solution (volts): ⫹1.356 Hazards and toxicity: For emergency response to a spill of chlorine, the immediate concerns are shown in the following box.

Immediate Concerns Hazard: Compressed, liquefied, greenish-yellow gas with an irritating odor. May react with other chemicals, causing fires and explosions. Fumes are very toxic. Humans: Severe irritant to skin, eyes, and respiratory system. May cause burns. Toxic by all routes, death may result. Environment: Toxic to aquatic life and harmful to the environment. Protection: Complete self-contained breathing apparatus recommended with face mask, suit, boots, and gloves. Human health: On inhalation, chlorine can cause irritation of the mucous membranes, watering of eyes, nasal discharge, sneezing, coughing, breathing difficulties, headaches, nausea, muscular weakness, and pulmonary edema. Liquid will burn skin and eyes on contact. Environment: Chlorine is toxic to aquatic life even in low concentrations and harmful to animals and vegetation. When moist, chlorine will react with many metals, e.g., brass, copper, aluminum, water, and turpentine. Behavior in air: Because chlorine gas is much heavier than air, it tends to settle in lowlying areas during spills. It may react with moisture to produce toxic and corrosive hydrogen chloride fumes, which often cause coughing in humans. Behavior in water: Slightly soluble in water. May react to produce hypochlorous and hydrochloric acid, raising the pH. Toxic to aquatic organisms.

33.3.3

Emergency Response

Move victim to fresh air and call for a doctor. Inhalation: If breathing is difficult or has ceased, give artificial respiration. Skin: Remove and isolate contaminated clothing and shoes at the site. In case of contact with material, immediately flush skin or eyes with running water for at least 15 minutes. Keep victim calm and monitor the temperature. Eyes: Should be well rinsed with large amounts of water for at least 15 minutes. Nose and mouth: Should be continuously flushed with large amounts of water.

33.6

CHAPTER THIRTY-THREE

Ingestion: Ingestion of chlorine is very rare. If it does occur, victims should be given large amounts of water to drink. Seek medical attention immediately. Spill Control: Self-contained breathing apparatus with full face mask should be worn for all emergency measures and total encapsulated suits for liquefied gas spills. Leaks: Call for emergency assistance. If leak is around valve stems, try to tighten the packing nut or packing gland. If leak does not stop, close container valve. If possible, reduce pressure in the container by removing the chlorine as a gas (not liquid). Move container to an isolated area. Fires: Chlorine itself does not burn or burns with difficulty. Try to extinguish fire with a drying agent well suited to the surrounding materials. Cool containers with large quantities of water. Use water spray to reduce vapor. Spills: Evacuate site. Avoid breathing vapors. Avoid bodily contact. Stay upwind. Provide ventilation. Soils: Flood site with copious amounts of water and neutralize with dilute sodium hydroxide, special foams, or soda ash. Keep away from water sources and sewers. Build barriers such as dikes, walls, and lagoons to contain spills. Water: Contain by damming or water diversion. Use dilute soda ash or sodium hydroxide to neutralize the water. Air: Knock down vapor with water spray or fine mist. Follow the emergency response guidelines (ERPG) of the American Industrial Hygiene Association as shown here (AIHA, 1988). Evacuate if concentrations are above guidelines. ERPG-3 ⫽ 20 ppm: The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing life-threatening health effects ERPG-2 ⫽ 3 ppm: The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms that could impair an individual’s ability to take protective action ERPG-1 ⫽ 1 ppm: The maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing other than mild, transient adverse health effects or without perceiving a clearly defined objectionable odor.

33.4

INDUSTRIAL ASPECTS AND PRODUCTION Chlorine is shipped as a liquefied compressed gas. Many grades of purity are available, such as high-purity grade with a minimum purity of 99.5%; ultrahigh-purity grade with a minimum purity of 99.9%; and research grade with a minimum purity of 99.96%. Since chlorine and caustic soda are produced by the same process, sales of caustic soda are dependent on chlorine production. However, caustic soda is not as great an environmental concern as chlorine. A large portion of the chlorine produced in Canada and the United States is for domestic use. Chlorine production reached its peak in 1982 and then started a downward trend. Some producers stopped production, and in 1989 chlorine capacity had to be expanded again. To date there are about 50 chloralkali plants in Canada and the United States with a total capacity of about 15 million tons / year of chlorine and 17 million tons / year of caustic soda. About 95% of total chlorine production is achieved by the electrolysis of brine, which also yields an almost equal amount of caustic soda. There are over 500 chloralkali producers

PERSPECTIVES ON SPECIFIC SUBSTANCES: CHLORINE

33.7

worldwide, with a nameplate capacity of 45 million tons of chlorine / year and 50 million tons of caustic soda. Demand for chlorine is quite stable, with only little or modest growth expected.

33.4.1

Manufacture of Chlorine

Over 95% of the world’s chloralkali production is achieved by the electrolysis of sodium chloride solution. The products are chlorine, caustic soda, and some hydrogen. The main types of electrolytic cells currently available are mercury, membrane, and diaphragm. The most commonly used in North America is the diaphragm cell (CIS, 1999). In Western Europe, the mercury cell is most commonly used, and in Japan the membrane cell is used because it requires much less energy. Industrially, chlorine is manufactured by the electrolysis of chloride salts (Curlin and Bommaraju, 1991). Three basic types of processes are used to produce chlorine, each process representing a different method of isolating the chlorine produced at the anode from the caustic soda and hydrogen produced at the cathode (Curlin and Bommaraju, 1991). Electrolytic processes currently in use are: 1. The diaphragm cell process (Griesheim cell, 1885) 2. The mercury cell process (Castner-Kellner cell, 1892) 3. The membrane cell process (1970) Chlorine is manufactured in Canada by the electrolysis of brine, which produces chlorine and caustic soda in about a 1:1.1 ratio, as well as some hydrogen. There are about 14 chloralkali plants in Canada, with a total nameplate capacity of about 1,293 kt per year. The ICI plant in Cornwall, Ontario produces caustic potash as well as chlorine, while the PGG’s plant at Beauharnois, Quebec, also produces sodium hypochlorite. Saskatoon Chemicals in Saskatchewan produces chloralkali and calcium hypochlorite. In the chloralkali electrolysis process, an aqueous solution of sodium chloride is decomposed electrolytically by direct current to produce chlorine, hydrogen, and sodium hydroxide according to the following equations: 2NaCl ⫹ 2H2O → Cl2 ⫹ H2 ⫹ 2NaOH

(33.1)

Evolution of chlorine takes place at the anode and is formed by the process: 2Cl⫺ → 2Cl ⫹ 2e⫺ → Cl2 ⫹ 2e⫺

(33.2)

While the basic electrolytic reaction in all three processes is the same, the methods for collecting chlorine generated at the anode are different. Each process represents a variation on keeping the chlorine produced at the anode separated from the caustic soda and hydrogen by-products. In all three processes, nearly saturated purified brine is introduced into the electrolytic cell at the beginning. Mercury Cell Process. The mercury cell process is not energy-efficient and is falling out of favor as a result of government regulations restricting the use of mercury. Less than 16% of Canadian chloralkali production currently uses mercury cells, and the process is gradually being phased out. In this process, sodium amalgam is produced at the cathode. The amalgam is reacted with water to produce hydrogen gas and caustic soda in a separate reactor, the decomposer. The brine is recirculated and charged with fresh solid salt. Very pure products are produced by this method. The reactions at the cathode are as follows:

33.8

CHAPTER THIRTY-THREE

Na⫹ ⫹ e⫺ ⫹ Hgx → NaHgx

(33.3)

2 NaHgx ⫹ 2 H2O → 2 NaOH ⫹ H2(g) ⫹ 2 Hgx

(33.4)

The mercury cell actually consists of two cells. The brine cell or electrolyzer is a long, slightly sloped trough containing purified brine. At the bottom of this trough is a thin sheet of metallic mercury that flows under the brine and constitutes the cathode. Projecting above the cathode is the anode assembly, which consists of horizontal blocks of graphite or titanium-based, dimensionally stable anode (DSA). During electrolysis, the brine is decomposed by the current passing through the electrodes to produce chlorine gas at the anode. The chlorine gas then leaves the anode assembly for purification. At the cathode, however, sodium ions are discharged to form a dilute sodium amalgam. The amalgam then leaves the cells and flows into the decomposer, which consists of vertical steel columns packed with graphite, where it reacts with water to form 50% caustic soda, hydrogen, and mercury. The sodium-free mercury is recirculated for reuse. These reactions can be illustrated by the following equations. Decomposer:

Na—Hg ⫹ H2O → NaOH ⫹ 1 / 2 H2 ⫹ Hg

Anode and cathode: 2NaCl ⫹ 2H2O → 2NaOH

(aq)

⫹ H2(g) ⫹ Cl2 (g)

Cathode

Cathode

(33.5) (33.6)

Anode

Because of mercury losses, the cathode has to be constantly topped up. The mercury cells pose an environmental hazard because mercury is constantly released into the air and effluents are released into water systems. Excessive formation of chloroorganic compounds is another concern with this process. Diaphragm Cell Process. The use of diaphragm cells to produce chloralkali has increased dramatically in recent years. The process now accounts for over 80% of chloralkali produced in Canada. In this process, the brine is fed into the anode compartment where chlorine is produced. The anode is separated from the cathode by a permeable asbestos-based diaphragm. Sodium ions pass through the diaphragm to the cathode, where sodium hydroxide is formed. The use of a diaphragm permits the free flow of ions and prevents the diffusion of electrolytic products. However, the sodium chloride solution can migrate through the pores of the diaphragm and the caustic soda can migrate back through the diaphragm to the anode. The end result is a mixture of caustic soda and sodium chloride. Some oxygen is also produced, which dilutes the chlorine and attacks the anode. Purified, saturated brine is fed in at the anode compartment. High voltage and hydrostatic pressure are required on the brine feed to allow a controlled rate of entry into the cathode. As the brine flows through the diaphragm into the cathode assembly, it undergoes electrolysis to produce chlorine, caustic soda, and hydrogen according to the following equation: 2NaCl ⫹ 2H2O → Cl2 ⫹ 2NaOH⫹ H2 Anode

Cathode

(33.7)

Cathode

A secondary reaction at the anode is the formation of oxygen as a result of decomposition of water and hypochlorous acid. Chlorine produced in this process is therefore often contaminated with oxygen. The chlorine is discharged at the dimensionally stable anodes and is collected with some oxygen and small amounts of hydrogen. Sometimes carbon dioxide is also produced as a result of oxidation of the graphite. Sodium ions migrate to the cathode, where hydrogen and hydroxide ions are also produced from the electrolysis of water. The hydrogen is removed from the cell and cooled to remove water. The cell liquor in the cathode contains about 10% caustic soda and 14% sodium chloride. The liquor is then concentrated in multiple-effect evaporators to produce a 50% caustic soda, with small amounts of salt. In the anode compartment, formation of hypochlorous acid is often suppressed by the addition of hydrochloric acid, which also neutralizes any hydroxyl ions that have back-

PERSPECTIVES ON SPECIFIC SUBSTANCES: CHLORINE

33.9

migrated. Many chlorinated and unchlorinated pollutants have been identified in the effluents of diaphragm cell plants. To overcome the disadvantages of the diaphragm cell, new ion-selective membranes have been developed to separate the anode and cathode. These new membranes allow the production of higher strength caustic and reduce the need for investment in downstream cleanup situations. The modified diaphragm is a mixture of asbestos and a fibrous fluorocarbon polymer. It is the most common diaphragm cell in use today. Membrane Cell Process. Less than 5% of chloralkali production in Canada is done using the membrane cell process. In this process, a cation-permeable ion-exchange membrane separates the anode from the cathode and only sodium ions and a little water can pass through the membrane. The brine is dechlorinated and recirculated, thus requiring solid salt for resaturation as in the mercury process. The chloride content in the caustic soda is similar to that in the mercury process. The chlorine gas is purified either by liquefaction or evaporation because it contains some oxygen. This is the most energy-efficient process, and there are no known environmental problems. The membrane cell represents a great improvement over the other processes from an environmental point of view. Mercury, asbestos, graphite particles, sodium sulfate, and sodium chloride often produced in the other processes are all eliminated. Production of chlorinated hydrocarbons is also reduced. In this process, a cation-exchange membrane such as perfluorocarboxylic acid membrane is used to partition the anode from the cathode assembly. The cation-exchange membrane allows only the hydrated positive ions, the sodium and hydronium ions, into the cathode compartment. The membrane also prevents the hydroxide ions generated in the cathode or chlorine ions in the anode from migrating across. Saturated brine is fed into the anode compartment but cannot pass through the membrane into the water-filled cathode assembly. Hydrogen is liberated at the cathode from the electrolysis of water. More water is often added to the cathode compartment to maintain a constant concentration. Some of the catholyte stream, which constitutes about 21% sodium hydroxide, is removed and concentrated. Chlorine gas generated at the anode is collected. In terms of environmental pollution, capital investment, and operating costs, the membrane process is preferred over the other processes. Environmental Concerns from Chlorine Use. The major environmental problem with chlorine is the chlorinated organic pollutants that are created in many processes in which it is used. Some of these byproducts are very toxic and persistent. For example, even though chlorine dioxide is now favored, several studies have reported that most pulp mills that use chlorine for bleaching discharge effluents that are acutely lethal to fish especially at point of discharge. On many occasions, effluents discharged into rivers do not dilute rapidly enough and kills of aquatic animals have been observed at locations far away from point of discharge. In 1989, Canadian pulp mills using chlorine bleached 678 tons of pulp per mill a day. It was estimated that about 86,000 tons of organic chlorine compounds were discharged into the receiving waters. Extremely high levels of dichlorophenols, trichlorophenols, trichloroguaiacol, and tetrachloroguaiacol have been detected in fish in the vicinity of effluent discharges. Chlorinated organic compounds are formed when chlorine used in bleaching the pulp reacts with phenols of the wood and humic substances during the pulping step. These pollutants are discharged with the effluents into the aquatic environment. It has been found that some of these effluents are lethal even at concentrations as low as 3.2% of the effluent. Chronic effects, including gross deformities, embryo and larval mortalities, behavioral modifications, and reproductive abnormalities, have been documented even at very low concentrations of effluent.

33.10

CHAPTER THIRTY-THREE

Environment Canada estimates that 100 to 150 g per year of 2,3,7,8-tetrachlorodibenzodioxin and 2,000 to 3,000 g per year of 2,3,7,8-tetrachlorodibenzofuran are discharged in bleached pulp mill effluents (Phenicie, 1993). It is estimated that only 10 to 40% of small chlorinated organic compounds in bleached pulp mill effluents have been identified. Some of the other substances detected are: chlorinated phenols, chlorinated acids, alcohols, aldehydes, ketones, sugars, aliphatic and aromatic hydrocarbons, trihalomethanes, chlorobenzenes, and aromatic thio ethers. Concentrations of individual chlorinated compound such as dichlorophenol, trichlorophenol, trichloroguaiacol, and tetrachloroguaiacol have been measured at 23%, 29%, 50%, and 95% of their respective LC50s. Toxicological effects of these effluent chloroorganics on fish and crustaceans include reduced gonad size, disorientation, high level of embryo and skeletal deformities, high parental and larvae mortality, steroid hormone imbalance, many physiological dysfunctions, disruptions in enzyme levels, liver enlargement, and fin and gill erosion. Another process of great concern involving chlorine is the production of chlorinated pesticides, plastics, and pharmaceuticals. Such pesticides include atrazine, oxychlordane, pentachlorophenol, and 1,1,1-trichloro-2,2-bis[4-chlorophenyl ethane (DDT)], all of which have now been banned. There is overwhelming evidence that DDT is responsible for reproductive failure in many birds and wildlife. Many of these substances are also extremely persistent and toxic and could disrupt the endocrine system of both wildlife and humans, resulting in dysfunctional development and behavior. Other similar chlorinated substances are polychlorinated biphenyls (PCBs) and their byproducts, such as polychlorinated dioxins and furans. In Germany and Austria, the use of polyvinyl chloride (PVC), which releases dioxins on burning, has been stopped. Another worrisome group of chlorinated substances is the chloroflurocarbons (CFCs), which are responsible for the destruction of the earth’s protective ozone layer. CFCs are being phased out gradually under the Montreal Protocol. Another area of concern is the use of chlorine in disinfecting water for drinking purposes. Known or suspected carcinogens that have been detected in samples of finished (chlorinated) drinking water are listed in the left column of Table 33.3 (Feige et al., 1980). Those compounds listed in the right column of the table are being investigated. Most of these substances are also found in chlorinated waste, sewage, cooling water, and pulp mill effluents. Health Canada has recommended a maximum acceptable level of 350 ␮g / L for trihalomethanes in drinking water. The U.S. EPA recommendation is 100 ␮g / L. Risk estimates for exposure to trihalomethanes at this concentration based on 2 L of water per day for a 70kg man is 1 in 2.5 million per year. Chloroform poses the highest cancer risk.

TABLE 33.2 Concentration Range and LC50s of Bleached Pulp Mill Compounds found in Biologically Treated Effluents from Kraft Pulp Mills

Compound

96 h LC50 (ppb)

2,4-Dichlorophenol Dichloroguaiacols Dichlorocatechol 2,4,6-Trichlophenol Trichloroguaiacols Trichlorocatechols Tetrachlorophenol Tetrachloroguaiacol Tetrachlorocatechol Pentachlorophenol Dehydroabietic acid Chlorodehydroabietic acid

2,800 2,300 500 to 1,000 450 to 2,600 700 to 1,500 1,000 to 1,500 500 200 to 1,700 400 to 1,500 200 500 to 2,000 600 to 900

Effluent concentration (ppb) 9 22 12 1 10 120

to to to to to to – 10 to 22 to – – 10 to

15 100 90 51 340 270 620 420 750

PERSPECTIVES ON SPECIFIC SUBSTANCES: CHLORINE

33.11

TABLE 33.3 Compounds Occurring in Drinking Water as a Result of Chlorination

Chloroform Bromodichloromethane Chlorodibromomethane Bromoform Dichloromethane Bis(2-chloroethyl) ether Trichloroethylene Tetrachloroethylene Chlorophenols

Trichloroacetic acid Trichloroacetaldehyde Chlorophenols Chlorobenzenes ␣-Chloroketones Chlorinated aromatic acids Chlorinated purines Chlorinated pyrimidines Nonhalogenated compounds

Food chlorination is another source by which chlorinated and nonchlorinated organics enter the human body. Chlorine is used to treat cake flour to prevent crumbling on removal from the oven. It has been estimated that over 1.5% of the total flour production in the United Kingdom is chlorinated. Trihalomethanes have also been detected in human milk and serum. Levels detected are 0.30 Ⳳ 0.032 ␮g / mL for human milk and 0.88 Ⳳ 0.012 ␮g / mL for the serum, thus showing the extensive burdens of these trihalomethanes in the human body.

33.4.2

Production in Canada, United States, and Worldwide

There are about 14 chloralkali plants in Canada and 36 in the United States, for a total of 50 (CIS, 1999). The total chlorine capacity in North America is about 15 million tons per year and 17 million tons per year of caustic soda. There are over 500 chloralkali producers worldwide, at more than 500 locations, and a total nameplate capacity of 45 million tons of chlorine per year and 50 million tons per year of caustic soda. In global terms, Dow Chemical is currently one of the largest chlorine producers, accounting for 13% of global production. More than 90% of this is used to make other products within the same company and most is used for domestic purposes. Dow has six manufacturing sites, with one in Canada, two in the United States, two in Germany, and one in Brazil. Chlorine prices often fluctuate in a relatively mature market. In 1998, prices declined by 30 to 40% as a result of a slump in the vinyl chloride industry and market prices have so far not improved. In the long-term, a modest growth of 1.5 to 2.5% per year has been predicted. New demands for polyvinyl chloride have been projected to grow at an above average rate of 5%. On the other hand, the pulp and paper industry will continue to use less and less chlorine for environmental reasons, and this may adversely affect the chlorine market. For example, the Canadian output for elemental chlorine-free pulp grew by 4% to 9.1 million tons in 1998, which is about 76% of the market and this trend is expected to continue. In 1998, in the United States, another 2.3 million tons of elemental chlorine-free pulp entered the market. These negative impacts will no doubt continue to grow except in the developing countries. The total nameplate capacity for chlorine in 1998 was 1,293 kilotons per year in Canada and 13,837 in the United States. Total imports to Canada in 1998 were 29 kilotons / year and 388 kilotons to the United States from all countries. The total supply of chlorine in Canada and the United States in 1998 was 1,049 and 12,073 kilotons / year respectively. The Canadian and American chlorine producers are listed here.

33.12

CHAPTER THIRTY-THREE

Canadian producer

Plant location

Avenor CXY Chemicals Canadian Occidental Canso Chemicals Dow Chemical Canada ICI Canada Norsk Hydro PCI Chemicals Canada PPG Canada St. Anne Chemical Sterling Pulp Chemicals

Dryden, ON Vancouver, BC Squamish, BC and Nanaimo, BC Abercrombie Point, NS Sarnia, ON, and Fort Saskatchewan, AB Cornwall, ON Becancour, QC Becancour, QC, and Dalhousie, NB Beauharnois, QC Nackawic, NB Saskatoon, SK

U.S. producer

Plant location

ASHTA Chemicals Bayer Dow Chemical DuPont Chemicals Elf Atochem NA Formosa Plastics Fort Howard General Electric Georgia Gulf Georgia Pacific Holtra Chem La Roche Chemicals Magnesium Corp. Occidental Chemical Olin Olin / Geon Oregon Metallurgical Pioneer PPG Industries Titanium Metals Vicksburg Chemical Vulcan Chemicals Westlake Polymers Weyerhaeuser

Ashtabula, OH Baytown, TX Plaquemine, LA, and Freeport, TX Niagara Falls, NY Portland, OR Two locations Three locations Mt. Vernon, IN, and Burkville, AL Plaquemine, LA Bellingham, WA Orrington, ME, and Acme, NC Gramercy, LA Rowley, UT Nine locations Four locations McIntosh, GA Albany, OR Three locations Two locations Henderson, NV Vicksburg, MS Three locations Calvert City, KY Longview, WA

The world consumes over 30 million tons of chlorine every year, with North America using the most (34.0%), followed by Western Europe (28.7), Eastern Europe (14.8%), Japan (8.5%), Asia (6.8%), and Latin America (4.3%). While some countries, such as the United States, the Western European countries, Brazil, Saudi Arabia, and Canada, export chlorine derivatives, others like Venezuela, Taiwan, Indonesia, Korea, Japan, Thailand, and South Africa do import some. The world’s chlorine consumption and capacity by region is shown in Table 33.4.

33.4.3

Transportation

Within the premises of a manufacturing plant, chlorine can usually be transported as a liquefied gas or a gas or transported by rail, road, or pipeline for several kilometers. In

PERSPECTIVES ON SPECIFIC SUBSTANCES: CHLORINE

33.13

TABLE 33.4 Chlorine Consumption and Capacity Worldwide

Region or country North America United States Canada Western Europe Eastern Europe Japan Asia and Pacific Latin America Middle East Africa

Consumption ⫻ 103 t

Total capacity ⫻ 103 t

12,050 10,240 1,810 11,540 6,840 3,930 3,390 1,790 680 460

11,710 10,340 1,370 9,890 5,110 2,940 2,350 1,500 590 420

commerce, chlorine is usually transported as a liquid either in small quantities in cylinders and drums or in bulk in railway tank cars, ton-containers, tank motor vehicles, and tank barges. While the capacity of railway tank cars ranges from 15 to over 90 tons, the road motor vehicle tank cars can carry only 15 to 20 tons. Barges are usually of the open-hopper type, with cylindrical, uninsulated pressure vessels with a total capacity of 600 to 1,200 tonnes. Some ships with a capacity of up to 1,000 tons are also specially designed to transport chlorine in Europe. Transport Canada and the Department of Transport (DOT) in the United States have developed regulations governing the design, construction, labeling, handling, loading and unloading, testing, and other specifications for containers carrying chlorine. The Chlorine Institute in the United States provides advice and information on handling and transportation of chlorine.

33.5

CHEMISTRY Chlorine is a very reactive element and its chemistry is extremely complex. It is a strong oxidizing agent and belongs to the halogen group in the periodic table. Its reactivity is determined by its seven electrons in the outer shell. A negatively charged chloride ion is formed when it gains one electron to complete its octet. Its various oxidation states are manifested by sharing one or more electrons with other elements. During chlorination of water, several complex reactions occur and the actual products of chlorination in raw water can never be predicted. The products that are formed, as well as their concentrations, depend not only on the chemical constituents of the water, which vary with the origin and time of the year, but also on the amount of chlorine added, temperature, pH, and reaction time. The reactions of dry chlorine are very different from those of wet chlorine. Chlorine can undergo the following four main types of reactions.

33.5.1

Hydrolysis

When chlorine is added to water, it rapidly hydrolyzes to produce hypochlorous and hydrochloric acids. The hypochlorous acid is rather unstable and generally regarded as the major reactive species, often assuming the role of an electrophilic reagent which can react with several naturally occurring compounds to form a wide variety of organochlorine compounds. Adding chlorine to seawater, however, does not result in the formation of hypochlorous acid but rather of hypobromous acid due to high concentrations of bromide ions in

33.14

CHAPTER THIRTY-THREE

seawater. Hypobromous acid is far more reactive than the sister hypochlorous acid. Hypochlorous acid and the hypochlorite anions are often referred to as free residual chlorine and are very toxic. The reactions of chlorine with water and of bromide with hypochlorous acid are illustrated in the following equations: Cl2 ⫹ H2O → HOCl ⫹ HCl

(33.8)

Br⫺ ⫹ HOCl → HOBr ⫹ Cl⫺ (seawater) 33.5.2

(33.9)

Addition Reactions

Dry chlorine and wet chlorine (hypochlorous acid) will react with organic substances containing double or triple bonds to yield vicinal dichlorides and chlorohydrins respectively. For example, hypochlorous acid will react with fatty acids in lipids such as oleic acid at pH 2 to 10, to produce 9-chloro-10-hydroxystearic acid, while dry chlorine will produce a mixture of chlorinated products. With fatty acids in plants and animals: CH3(CH2)7 CH⫽CH (CH2)7 COOH ⫹ HOCl →

(33.10)

Oleic acid

CH3(CH2)7 CHCl—CHOH (CH2 )7 COO 9-Chloro-10-hydroxystearic acid

CH3(CH2)7 CH⫽CH (CH2)7 COOH ⫹ Cl2 Oleic acid

↓

(33.11)

CH3(CH2)7

CHCl—CHCl (CH2 )7 COOH

9,10-dichlorostearic acid

With sulfur dioxide and carbon monoxide in the air, dry chlorine also reacts to give sulfuryl chloride and carbonyl chloride or phosgene respectively.

33.5.3

SO2 ⫹ Cl2 → SO2Cl2

(33.12)

CO ⫹ Cl2 → COCI2

(33.13)

Oxidation Reactions

As has been pointed out, chlorine is a strong oxidizing agent. Oxidation is the most predominant type of reaction that occurs between hypochlorous acid and all the naturally occurring organic constituents of water and wastewater (Ghanbari et al., 1982; Helz et al., 1978; Jolley and Carpenter, 1983; NRC, 1979; Rook, 1980). The most common example of this group is the oxidation of alcohols, phenols, and aldehydes to their corresponding ketones, aldehydes, or acids. The oxidation products of phenols by chlorine in pulp and paper can further condense to produce substances like dioxins. RCHO ⫹ HOCl → RCOOH ⫹ H⫹ ⫹ Cl⫺

(33.14)

RCHOHR ⫹ HOCl → RCOR ⫹ H2O ⫹ H ⫹ Cl 1

33.5.4

1

⫹

⫺

(33.15)

Substitution Reactions

Chlorine reacts vigorously with amines and ammonia. Both wet and dry chlorine react with many aromatics, aliphatics, and amines.

PERSPECTIVES ON SPECIFIC SUBSTANCES: CHLORINE

Cl2 ⫹ 4 NH3 → NCl3 ⫹ 3 NH4Cl

33.15

(33.16)

Chlorine reacts with amine or ammonia constituents in water or in air, often replacing the hydrogens. Formation of chloramines, trihalomethanes, and other chlorinated organic compounds during natural water chlorination and wastewater treatment are the result of substitution reactions, as illustrated by the following equations: RNH2 ⫹ HOCl → RNHCl ⫹ H2O

(33.17)

Further substitution can occur to give the di- and trichloramines. RCOCH3 ⫹ 3HOCl → RCOOH ⫹ CHCl3 ⫹ 2H2O

33.5.5

(33.18)

Reactions with Specific Chemicals

Chlorine will also react with the following chemicals: ammonia, acetylene, butadiene, benzene, hydrogen, sodium carbides, turpentine, and finely divided powdered metals. In some cases, these reactions may be violent and explosive mixtures may be formed.

33.6

ENVIRONMENTAL FATE When chlorine is released into the air from a container, liquefied chlorine expands 470 times to the gaseous phase. It is quickly dispersed and at a faster rate by air motion if a strong wind is blowing. Chlorine is heavier than air and can accumulate in low-lying regions. Under wet conditions it is quickly hydrolyzed, or, in bright sunlight, it is photolyzed to form chlorine radicals. Some heavy vapor dispersion models for chlorine have been developed and found deficient. Some models are deficient because methods used to estimate the dispersion of heavy gas clouds apply to the case of dispersion over flat, uninterrupted terrains. It has always been assumed that the concentration-time profile follows the ‘‘top-hat’’ behavior. Once released into the environment, chlorine can undergo some of the reactions discussed in Section 33.5. The most important reaction is the formation of chlorides and hypochlorites with water which will eventually end up in the soil or water bodies. Many chlorine derivatives, including chlorofluorocarbons, can be transformed into a variety of compounds, mostly through oxidation and photolysis by visible solar radiation to produce oxidized species and chlorine radicals respectively. Chlorine radicals are of great interest because they have been specially implicated in the depletion of the ozone layer, as shown with the following equations: RCl ⫹ h␯ → R 䡠 ⫹ Cl䡠

(33.19)

Cl2 ⫹ h␯ → 2Cl䡠

(33.20)

HCl ⫹ OH. → Cl 䡠 ⫹ H2O

(33.21)

1 / 2Cl2 ⫹ O2 ⫹ M ↔ ClOO ⫹

(33.22)

Cl䡠 ⫹ O3 → ClO䡠 ⫹ O2 ozone removal step

(33.23)

Cl2F2C ⫹ h␯ → Cl䡠 ⫹ 䡠ClF2C etc.

(33.24)

Increased ambient concentrations of organochlorine compounds, including chlorofluoromethanes (freons), carbon tetrachloride, and chloroorganic compounds, constitute a great

33.16

CHAPTER THIRTY-THREE

hazard to the ozone layer. The chlorofluorocarbon radicals are very stable and can persist for a very long time.

33.7

BEHAVIOR Chlorine is about 2.5 times heavier than air and on release will generate vapor clouds that remain close to the ground. According to the Chlorine Institute in the United States, a failure of a 1-in. chlorine gas line with an infinite supply of chlorine generating a chlorine cloud containing in excess of 25 ppm will travel from 304.8 to 1,219.2 m (1,000 to 4,000 ft), depending on atmospheric conditions. If the valve is struck and sheared off a one-ton container, a cloud will be produced containing in excess of 25 ppm and will travel from 914 to 3,352.8 m (3,000 to 11,000 ft), depending on atmospheric conditions. A 90-ton chlorine tank car derailment with a puncture that produces a chlorine cloud containing in excess of 25 ppm will travel from 1,828.8 to 5,486.4 m (6,000 to 8,000 ft), depending on atmospheric conditions. The behavior and impact of an accidental release of chlorine can be estimated by three groups of models: 1. Emission rate models, which focus on the chemical as it is being released from its container into the air 2. Dispersion models, which predict the downwind concentrations and distances as a function of time 3. Risk assessment models, which analyze the toxicity and exposure of a chemical to a specific receptor

33.8

HUMAN AND ENVIRONMENTAL TOXICITY During accidental spills, exposure to chlorine is often moderate and short-term in nature due to chlorine’s pungent odor. Full recovery often occurs. Also, chronic to low-level exposures, as often occur in occupational settings, do not seem to produce any long-term toxic effects. Some symptoms of irritation and coughing have been reported, however, after hours or days of exposure. No serious risks such as mutation, cancer, reproductive, and development impairment have been documented. Contact with liquefied chlorine will definitely cause frostbite, burns, ulcerations, or necrosis. A concentration of 1,000 ppm by volume of chlorine in air is rapidly fatal after a few deep breaths. The least amounts that will result in throat irritation and coughing are 15 and 30 ppm respectively. The maximum level that can be inhaled for one hour without serious effects is 5 ppm. Concentrations of 3 to 5 ppm by volume in air are readily detectable. The effects of different concentrations of chlorine on humans are shown in Table 33.5. The maximum exposure levels of chlorine according to various guidelines are shown in Table 33.6.

33.9

SURVEY OF PAST SPILLS, LESSONS LEARNED, AND COUNTERMEASURES APPLIED Most chlorine spills reported in Canada involve small volumes. For example, 25% involve volumes of less than 10 L and about 50% have some environmental or human impact. Spills

PERSPECTIVES ON SPECIFIC SUBSTANCES: CHLORINE

33.17

TABLE 33.5 Effects of Chlorine on Humans

Concentration (ppm)

Effects

1 3.5 4 15 30 40 to 60 1,000

Minimum concentration causing slight symptoms after several hours Minimum concentration detectable by odor Maximum concentration that can be breathed for one hour without damage Minimum concentration causing throat irritation Minimum concentration causing coughing Concentration dangerous in 30 minutes Concentration likely to be fatal after a few deep breaths

from manufacturing and processing facilities account for over 50% of reported spills. Because equipment failure and operator error are the major reasons for spills, spills could probably be prevented by proper equipment maintenance and staff training.

33.9.1

The Mississauga Train Derailment, 1979

The largest chlorine spill in Canada occurred in November 1979. The following is a summary of the accident report (Grange, 1980). Twenty-four cars from a CP Rail train derailed in Mississauga, Ontario. The cars were carrying chemicals, including toluene, propane, and chlorine. Fire spread through most if not all of the derailed cars. Those loaded with propane exploded and considerably damaged neighbouring property. The accident was caused by a fault in a lubricator pad, which caused the bearing and journal to come in direct contact, the bearing to subsequently overheat, and a tank car to collapse, causing the derailment. The emergency response team arrived at the scene six and a half hours after the accident occurred. A smell of chlorine was detected immediately on arrival at site, but the team was

TABLE 33.6 Maximum Exposure Level Guidelines

Guideline

Concentration and time

Threshold limit value (TLV) Short time public exposure limit (STPL)

1 ppm. Time-weighted average for 8-hour working day 1 ppm for 10 minutes 0.5 ppm for 30 minutes 0.5 ppm for 60 minutes 3 ppm for 10 minutes 2 ppm for 30 minutes 2 ppm for 60 minutes 7 ppm for 5 minutes 5 ppm for 15 minutes 4 ppm for 30 minutes 3 ppm for 60 minutes 0.5 ppm for 24 hours 0.1 ppm for 90 days 1 ppm (ERPG-1) 3 ppm (ERPG-2) 20 ppm (ERPG-3)

Public exposure limit (PEL)

Emergency exposure limit (EEL)

Continuous exposure limit (CEL) Emergency response planning guidelines (ERPGs)

33.18

CHAPTER THIRTY-THREE

unable to locate the exact car, even with a helicopter. The Ontario Ministry of Energy and Environment analyzed chlorine levels in the area and found very low concentrations. Due to fear of the chlorine escaping, however, almost a quarter of a million people were evacuated from their homes and businesses for periods of up to five days. When the tank car carrying the chlorine was finally located, it was found to have a 2.5-ft hole in its outside covering and was covered with a tarpaulin. A command post was set up and manned by staff of the Attorney General. When the fire died down, the response team attempted to patch the hole with a Proctor patch and to empty the car of its chlorine contents. When pressure was applied, the patch did not hold. The tank car was finally repaired three and a half days after the accident. Technical personnel from Canadian Industries Limited vacuumed out the chlorine as opposed to pressurizing the tank car. The liquid was removed to a tank truck and then to a tank car and the chlorine vapor was neutralized with caustic soda. Lessons to Be Learned. The Commission of Inquiry concluded that the response team sent by the chemical company were not qualified or adequate. They did not know how much chlorine remained in the tank car after the initial escape and did not know how to calculate it. They failed to take measures to vent the car at the beginning to prevent chlorine from escaping. They did not know how to empty the chlorine from the tank cars. Furthermore, the response team incorrectly instructed the firefighters at the scene to water the chlorine car, and in fact team members watered the tank car themselves. And finally, the response team gave poor advice to the command post team, particularly with regard to the rate of vapor and liquid being emptied, the method of emptying the chlorine from the tank car, and the dangers of release of gas after ice was broken.

33.9.2

Chlorine Leak at Pioneer Plant, 1991

Officials at Pioneer Chlor Alkali Co., Inc. near Henderson, Nevada, investigated an accidental chlorine leak early one morning. The chlorine gas leak was detected by the air monitoring system about 1:10 a.m. and the 10 employees working at the time were evacuated by 2:30 a.m. As a precaution, many residents were evacuated until the chlorine gas dissipated later in the morning. The accident apparently began when a narrow tube in the heat exchanger, which kept the chlorine’s temperature low as it was converted from gas to liquid, broke and water coolant leaked into the chlorine. Much of the water–chlorine mixture travelled into one of the eight 150-ton storage tanks. Chlorine and water, which mix to make hydrochloric acid, corroded a hole in a discharge pipe coming out of the storage tank. Employees closed the valve on the tank to stop the flow of chlorine through the corroded hole. But the water and chlorine in the storage tank corroded at the tank valve and the valve did not hold. The chlorine and water mixture continued to leak until a piece of metal was blinded into the pipe at about 7 a.m. No serious injuries were reported in this incident. Lessons to Be Learned 1. This incident demonstrated the need for fail-safe equipment systems and new technologies using stainless steel equipment. 2. Preventive maintenance must be carried out on critical process equipment and vessels.

PERSPECTIVES ON SPECIFIC SUBSTANCES: CHLORINE

33.19

3. Early warning signs are necessary when such failures occur. 4. Emergency response needs to be improved, i.e., it should not have taken more than 30 minutes to evacuate 10 employees.

33.10

REFERENCES American Industrial Hygiene Association (AIHA). 1988. Emergency Response Planning Guidelines— Chlorine, AIHA, Akron, OH. Bailar, J. C., H. J. Emeleus, R. Nyholm, and A. F. Trotman-Dickenson. eds. 1975. ‘‘Halides,’’ in Comprehensive Inorganic Chemistry, Pergamon Press, New York, NY, pp. 1124–1280. Braker, W. and A. L. Mossman. 1980. ‘‘Chlorine,’’ in Matheson Gas Data Book, Matheson, Gas Products, East Rutherford, NJ, pp. 155–159. Camford Information Services, Inc. (CIS). 1999. ‘‘Chlorine,’’ in CPI Product Profiles, CIS, Scarborough, ON. Compressed Gas Association, Inc. (CGA). 1990. Handbook of Compressed Gases, 3rd ed., Van Nostrand Reinhold, New York, NY, pp. 231–232. Curlin, L. C. and T. V. Bommaraju. 1991. ‘‘Alkali and Chlorine Products,’’ in Encyclopedia of Chemical Technology, ed. M. Howe-Grant, 4th ed., vol. 1, John Wiley & Sons, New York, NY, pp. 938–1025. Environment Canada. 1999. National Analysis of Trends in Emergency Situations (NATES): Chemical Accidents Reports Database, Hull, QC. Feige, M. A., E. M. Glick, J. W. Munch, D. J. Munch, R. L. Noschang, and H. J. Brass. 1980. ‘‘Potential Contaminants Introduced into Water Supplies by the Use of Coagulant Aids,’’ in Water Chlorination Environmental Impact and Health Effects, ed. R. L. Jolley, W. A. Brungs, R. B. Cumming, and V. A. Jacobs, Ann Arbor Science Publishers, Ann Arbor, MI, pp. 789–799. Fingas, M., N. Laroche, G. Sergy, B. Mansfield, G. Clouthier, and P. Mazerolle. 1991. ‘‘A New Chemical Spill Priority List,’’ in Proceedings of the Eighth Technical Seminar on Chemical Spills, Environment Canada, Ottawa, ON, pp. 223–237. Ghanbari, H. A., W. B. Wheeler, and J. R. Kirk. 1982. ‘‘Reactions of Aqueous Chlorine and Chlorine Dioxide with Lipids: Chlorine Incorporation,’’ Journal of Food Science, vol. 47, pp. 482–485. Grange, S. G. M. 1980. Report of the Mississauga Railway Accident Inquiry, Supply and Services, Hull, QC. Helz, G. R., R. Sugam, and R. Y. Hsu. 1978. ‘‘Chlorine Degradation and Halocarbon Production in Estuarine Water,’’ in Water Chlorination: Environmental Impact and Health Effects, ed. R. L. Jolley, H. Gorchev, and D. H. Hamiltion, Jr., vol. 2, Ann Arbor Science Publishers, Ann Arbor, MI, pp. 209– 222. Jolley, R. L., and J. H. Carpenter. 1983. ‘‘A Review of the Chemistry and Environmental Fate of Reactive Oxidant Species in Chlorinated Water,’’ in Water Chlorination: Environmental Impact and Health Effects, ed. R. L. Jolley, W. A. Brungs, J. A. Cotruvo, R. B. Cumming, J. S. Mattice, and V. A. Jacobs, vol. 4, bk 1, Ann Arbor Science Publishers, Ann Arbor, MI, pp. 3–47. Lide, D. R., ed. 1999. CRC Handbook of Chemistry and Physics, 80th ed. CRC Press, New York, NY. Nuclear Regulatory Commission (NRC). 1979. The Chemistry of Disinfectants in Water, Reactions and Products, PB-292776, U.S. Department of Commerce, Washington, DC. Perry, R. H., D. W. Green, and J. O. Maloney, eds. 1984. Perry’s Chemical Engineer’s Handbook, 6th ed. McGraw-Hill, New York, NY. Phenicie, D. K. 1993. Virtual Elimination in the Pulp and Paper Industry, Report to the Virtual Elimination Task Force. Rook, J. J. 1980. ‘‘Possible Pathways for the Formation of Chlorinated Degradation Products during Chlorination of Humic Acids and Resorcinol,’’ in Water Chlorination: Environmental Impact and Health Effects, ed. R. L. Jolley, W. A. Brungs, and R. B. Cumming, vol. 3, Ann Arbor Science Publishers, Ann Arbor, MI, pp. 85–98. RTECS On-Line. 2000. Registry of Toxic Effects of Chemical Substances, Department of Health and Human Services, Centers for Disease Control, National Institute for Occupational Safety and Health, Washington, DC.